Date indicating mechanism for watches

ABSTRACT

A date indicating mechanism for watches, of the type having a rotatable ring carrying date numbers on one side, equidistantly spaced over the circumference thereof, and means for periodically moving the ring past an inspection window for the date numbers, the improvement comprising drive means for the ring carrying the date numbers, said drive means consisting of a rotatable disk carrying pins meshing with slits provided on one edge of the date number ring and with engagement means on the periphery of a substantially circular cam driven by the gear train of the watch.

United States Patent Dome [451 Dec. 5, 1972 [5 DATE INDICATING MECHANISM FOR FOREIGN PATENTS-OR APPLICATIONS WATCHES 172,591 ll/l92l Great Britain ..58/58 lnvemori r s Dome Bmgg bei Biel, Switzef- 1,042,477 10 195 Germany ..ss/ss [73] Assignee: Societe Suisse pour IIndustrie Hor- Primary Examiner-George Miller,

T logere SA, Geneve, Switzerland At torney-Karl F. Ross 22 F'l d: .31 1972 l 1 Jan 57 ABSTRACT [21] Appl. No.: 222,260

A date indicating mechanism for watches, of the type having a rotatable ring carrying date numbers on one [30] Forelg Apphcatlon Pnomy side, equidistantly spaced over the circumference Feb. 5, 1971 Switzerland ..1722/71 th r f, and m ans f r p ri di ally moving the ring past an inspection window for the date numbers, the [52] US. Cl. .,58/58 improvement comprising drive means for the ring car- [5 l 1 II."- Cl. .l: rying the date numbers drive means consisting of [58] Field of Search "58/4 R, 4 A, 5 58 a rotatable disk carrying pins meshing with slits vided on one edgeof the date number ring and with [56] References C'ted engagement means on the periphery of a substantially UNITED STATES PATENTS circular cam driven by the gear train of the watch. 3,367,104 2/1968 Rogers ..,....58/58 2 Claims, 9 Drawing Figures PATENTED 5 I972 3. 704, 583

sum 1 or 2 a 1 DATE lNDlCATlNG MECHANISM FOR wx'rcnss This invention relates to a date indicating mechanism for watches, of the type having a rotatable ring carrying on one'side n date numbers equidistantly spaced over the entire circumference of the ring and means for periodically the ring through an angular distance corresponding to 360ln past an inspection window permitting the date numbers on the ring to be individually and successively observed.

Many date indicating mechanisms of this type are already known, they being designed mainly for mechanically operated watches in which the date numbers carried by a movable member appear successively in the inspection window. The position of the movable member is generally determined by a spring locking member which successively engages between the teeth of a toothed edge provided on the movable member as the latter is rotated step by step. During the daily operation of the 'movable member the driving member must therefore overcome the spring force of the locking member to disengage it from the toothed edge. The power required for this purpose is derived directly from the wheel train'of the watch and thus must be supplied by the watch drive spring.

if this slight loss of power may be tolerated in this type of watch in which the drive power is supplied by a drive spring which is either manuallyor automatically wound up from time to time, it is different with electromechanically and electronically driven wrist watches in which this loss of power causes a considerable reduction of the useful life of the supply battery. Further, since there is very little space available in such wrist watches supply batteries must necessarily be small and consequently power consumption must be reduced to a minimum to permit the produced watches to be sold and to compete on the market with other watches, particularly mechanically drivenwatches/adapted to be wound'up automatically. i

This is certainly'one of the reasons why the conventional date indicating mechanisms, although they have already been tested for many years, have not been generally adopted in electromechanically or electronically driven wrist watches.

As is known, these watches are all provided with an electric circuit generating current pulses each carrying a minute quantity of power and designed either to control' a mechanical regulating device or drive a motor.

By adding a date indicating mechanism to such watches, the regulating device or motor must also drive this mechanism in addition to the time indicating means and then this mechanism constitutes a frequent source of faults caused mainly by the spring locking member.

. To eliminate this drawback a date indicating mechanism has already been proposed in which a Maltese cross wheel is rotatably mounted on an axle extending perpendicularly to the plane of the date number ring and is driven by the hour hand wheel through a drive wheel making one complete revolution every 24 hours. This Maltese cross wheel is provided with a pin engaging in slits provided on the date number ring, and with a circle segment member cooperating with concave surfaces provided on the teeth located between said slits. Thus the segment member secures the date number ring in the required position.

In this form of construction positioning of the date number ring is effected by engagement by two concentric surfaces carried by two movable members, i.e., the Maltese cross wheel and the date number ring, which are eccentrically mounted with,respect to each other. As the date number ring is generally not supported for pivotal movement about a shaft its center of rotation is usually determined by a circular bearing surface provided on the bearing plate of the watch so as toengage the date number ring.

This manner of providing for rotary movement of the date number ring of course makes it necessary to leave a certain amount of play between the date numberring and its centering bearing surface on the bearing plate of the watch to avoid seizing. This is the reason why in this form of construction the Maltese cross is supported on a rocker lever urged by a spring against the date number ring to eliminate the play and ensure intimate engagement between the two concentric positioning surfaces. By pressing these surfaces together considerable friction is produced during rotation of the Maltese cross wheel. Consequently, although this form of construction has permitted to eliminate the source of faults caused by the locking member in the conventional construction, this proposed new structure has another even greater drawback which is the relatively high friction produced between the positioning surfaces.

It is the object of the present invention to eliminate the above-mentioned drawbacks of the hitherto proposed constructions. This object is achieved according to the invention by providinga date indicating mechanism for watches, in which the drive means comprise:

a series of n slits equidistantly spaced around the circumference of a date i number ring, said slits being open at one edge of the date number ring and having parallel longitudinal edges, a longitudinal axis oriented toward the center of the date number ring, and -a radial length substantially corresponding to half the distance between the two points of intersection between the two opposed longitudinal edges of two adjacent ones of said slits and the edge of the date number ring containing the open ends of said slits; I

a disk located in a plane extending parallel to the plane of the date number ring and rotatably mounted on a shaft centered substantially at right angles to the edge of the date number ring containing the open ends of said slits, said disk carrying four equidistantly angularly spaced pins each spaced from the axis of said shaft by a distance substantially corresponding to half the distance between the two points of intersection of the two adjacent longitudinal edges of two neighboring ones of said slits in the date number ring with the edge of the latter containing the open ends of said slits, the width of said pins being substantially equal to that of said slits and two of said pins, located in diametrically opposed positions on said disk with respect to the axis of rotation thereof, having a projecting portion of a length at least greater than the distance between the adjacent surfaces of said date number ring and said disk, the other two of said pins having a projecting portion of a length smaller than said distance; a rotatable cam located in a plane extending parallel to the plane of the date number ring and having an operative profile composed of a first and a second portion, said first portion extending in a circular direction around the axis of rotation of said rotatable cam and being designed for locking the date number ring in one of its n angular positions, the axis of rotation of said rotatable cam being positioned so that said first portion of the rotatable cam will engage two neighboring ones of said pins on 'said disk, said second portion of the rotatable cam being designed for moving the date number ring from a given angular position to the next one and including a radial projection having a width corresponding at most to thedistance between two neighboring ones of said pins, and two recesses arranged one on each side ofthe radial projection and having a width at least corresponding to that of said pins, and a kinematic chain formovin'g'said rotatable cam by one revolution each 24 hours from the gear train of the watch. 7

-A.preferred embodiment of the invention will now be described by way of example and with preference to the accompanying drawings, in which:

FIG. 1 is a top plan view of a date indicating mechanism according to the present invention; FIG. 2 is a section taken on the line 11-11 of FIG. 1;

' FIGS. 3 to 8 are part views of FIG. 1, showing different positions of the date number ring, pin supporting disk and rotatable cam, and i I" FIG. 9 is a part view showinganother embodiment of respectively, substantially corresponds to the distance between the longitudinal axes of symmetry between two neighboring slits 4 as measuredat the level of the inner edge of the date number ring 1.

Finally, the length of the projecting portion of the two pins 8A and 8B is greater than the distance between the top of the disk 5 and the bottom of the annular portion 1A of the date number ring 1 whereas the length of the projecting portion of the two pins 7A and 7B is smaller than this distance, as seen in FIG. 2. Therefore, when the disk 5 is rotated around the axis of the shaft 6, for example, in clockwise direction, the pins 8A and 8B will mesh with the teeth between the slits 4 in the annular portion 1A of the date number ring 1 whereas the pins 7A and 7B will pass below the lower surface of this portion 1A without touching it.

In the illustrated embodiment the two pins 8A and 8B are made of ferromagnetic material as is the entire date number ring 1 whereas the disk 5 and the pins 7A and 7B are preferably made of non-magnetic material. The pins 8A and 8B as well as the sector of the date number ring .1, delimited roughly by two straight radial lines tangent to the disk 5 in diametrically opposed the date number ring, pin supporting disk and rotatable cam.

The mechanism shownin the drawings is designed to produce at about 24.00 hours of each day a substitution of the indication of the date number appearing inan inspection window G provided in a dial C of a watch.

As shown, in FIG. 1, this mechanism comprises a date number ring 1 composed of two portions, namely a first annular portion 1A carrying on its upper face the numbers 1 through3l corresponding to the number of days in a month, and-a second cylindrical portion 18 supporting the date number ring I on a seat 2A provided on a bearing plate 2 of the watch, the seat 2A having an annular'shape and extending symmetrically around a shaft 3 carrying the hour hand of the watch the rest of whichis not shown in the drawings as it does not relate to the present invention. v

Along its inner edge the date number ring 1 is pro.- yided with 31 equidistantly spaced-slits 4 each having two parallel longitudinal edges and an axis of symmetry oriented toward the center of the date number ring 1. The radial length of each slit 4 is slightly greater than half the distance between the ends a and b of the opposed longitudinal edges of two neighboring slits 4.

The illustrated date indicating mechanism further comprises a disk 5 rotatably mounted on a shaft 6 whose longitudinal axis extends substantially at right angles relative to a point on the inner edge of the date number ring 1, the shaft 6 being secured in the bearing plate 2. The disk 5 carries four pins 7A, 78, 8A and 8B having a diameter substantially corresponding to the width'of the .slits 4 in the date number ring 1 and symmetrically arrangedin opposed pairs on the disk 5 with respect to the shaft 6-.

The pins 7A, 78, 8A and 8B are secured in the disk 5 in the manner shown in FIG. 2 with reference to the pin 78 and their lower ends are flush with the bottom surface of the disk 5. The distance between the axes of syrnrnetry of the pins 7A and 7B and 8A and 83,

positions of the latter, form part of a magnetic circuit including a permanent magnet 9, secured to the hearing plate 2 adjacent the cylindrical skirt 1B of the date number ring 1 and an L-shaped magnetizable armature l0 engaging the magnet 9 with its shorter leg and the bearing plate 2 with its longer leg which rests on the bearing plate 2 and extends in part below the disk 5 and thus facesthe lower ends of the pins 8A and 8B irrespective of the angular position of the disk 5 so that the air gap between these pins and the armature 10 will remain always the same. The purpose of this magnetic circuit will appear from the following description.

The illustrated date indicating mechanism further comprises a rotatable substantially circular cam 11 firmly secured to a gear wheel 12 and rotatably mounted on a shaft l3-extending upwardly-from the mounting plate 2 in a position such that the plane passing through the longitudinal axes of the shafts 13 and .6 forms a dihedral angle with the plane passing through the longitudinal axis of the shaft 6 and that of the shaft 3. r I

I The gear wheel 12 is driven by a gear wheel 14 mounted on the shaft 3 and driven directly by a gear wheel 15 of the hour hand of the watch. The diameter of the gear wheel 12 and that of the gear wheel 14 are so chosen that the circular cam 11 will make one complete revolution every 24 hours.

As seen in FIG. 1, the circular cam 11 engages with its circular edge portion two pins on the disk 5, which in the position of the disk 5 shown in FIG. 1 are the pins 7A and 8A, so that the disk 5 cannot move angularly in either direction of rotation. In this position of the disk 5 the pins 8A and 8B engage in two slits 4 in the date number ring 1 and as the diameter of these pins substantially cornesponds to the width of the slits 4, they ensure perfect locking of the date number ring 1 in its angular position provided that the disk 5 itself remains locked by the circular cam 1 1.

However, to ensure such locking the dimensions of the slits 4 in the date number ring 1, the angular spacing of the slits 4, the dimensions of the pins 8A and 88 as well as their positions on the disk 5 and the position of-the disk 5 on the bearing plate 2 must be very accurate. Such accurate dimensions can be achieved in practice but .in the illustrated embodiment it is not indispensable, particularly in view of the action exerted by the permanent magnet 9 and the magnetic circuit in which this magnet is incorporated and which has been described above.

In fact, supposing that the width of the slits 4 is slightly greater than the diameter of the pins 8A and 8B, in which case there would be some play between the pinsand the edges of the slits so that the date number ring 1 could performa slight angular move ment, this play is compensated in the illustrated embodiment by the action of the magnetic circuit since the pins 8A and 8B as well as the date number ring 1 are traversed by magnetic flux and consequently at least one of these pins is magnetically attracted toward one of the longitudinal edges of the slit in which it is located and thus firmly engages that edgeof the slit.

As shown in FIG. 1, the periphery of the circular cam l is not completely circular. In fact, a length of about I] IQ of the circumference of the earn 1 is occupied by two recesses 16 and 17 and a projection 18 located between the recesses 16 and 17. The projection 18 has a substantially trapezoidal shape, its width at the top is slightly smaller than the distance between two adjacent ones of the pins 7A, 8A, 7B and 8B on the disk 5 and its length is such that it does not engage the shaft 6, for example, during angular movement of the circular cam 11 from the position indicated in FIG. 4 to that shown in FIG. 6.

The recesses 16 and 17 each have an approximately semicircular shape, a width slightly greater than the diameter of the pins 7A, 78, 8A and8B and a depth slightly greater than half the diameter of the pins. The circular cam 11, in fact, does not only serve the purpose of locking the disk 5 as described above, but also serves for periodically moving the disk 5 once during each revolution of the circular cam 11, through an angular distance of 180 which=corresponds to a movement of the date number ring 1 through an angular distance of 360l3l i.e., the distance required to replace a date number appearing in the inspection window G of the dial C by the following date number, as will be explaine hereafter by reference to FIG. 1 and FIGS. 3 through 8 of the drawings.

In the illustrated embodiment the circular cam 11 is driven by the gear wheel 14 in an anticlockwise direction. As the circular cam 11 engages with its circular peripheral portion the pins 8A and 8B,the disk 5 and consequently the date number ring'l are locked in their positions indicated in FIG. 1. This condition is maintained until the projection 18 engages the pin 7A, as shown in FIG. 3, for thereafter the disk 5 in moved in a clockwise direction by the projection 18, as seen in FIG. 4. As the disk 5 further has its pins 8A and 8B meshing with the teeth 1C of the date number ring 1, angular movement of the disk-5 will produce a corresponding angular movement of the date number ring 1. particularly through the action of the pin 8A which moves angularly in a circular path and simultaneously penetrates more deeply into the interior of the slit 4 in which it is located (FIG. 1), and exerting a pressure on the edge of this slit 4 which in the drawing is located on the right.

If the speed of rotation of the circular cam 11 is constant, the angular movement of the date number ring 1 follows a sinusoidal course. This the speed of angular movement of the date number ring 1 is relatively small when the projection 18 begins to exert its pressure on the pin 7A, as shown in FIG. 3, and gradually increases as the projection 18 approaches its position shown in FIG. 5, in which position the longitudinal axis of the projection 18 is in alignment with the plane'passing through the axes of simmetry of the shaft 13 and 6 and consequently the pin 8A occupies its position located most closely to the bottom of the slit 4 in which it is engaged. Thus the speed of angular movement of the date number ring 1 is greatest when this ring passes through the position shown in FIG. 5 and thereafter it decreases until it is reduced to zero. 1

1 Once the circular cam 11 has passed beyond the position shown in FIG. 5 there will come a moment when the pin 7A has moved sufficiently away from the projection 18 so that the latter can no longer shift the pin 7A. However, movement of the disk 5 continues due to the pressure exerted by the edge of the recess 17 on the pin 8B located in this recess when the pin 7A separates from the projection 18, as shown in FIGS. 6 and 7. The movement of the disk 5 does not stop until the pin 8B is in the position occupied by the pin 8A in FIG. 1 or until the pin 8A is in the position occupied by the pin 8B in FIG. 1.

The dimensions of the circular cam 11, projection 18, recesses 16 and 17 and the transmission ratio of the gear wheels 12 and 14 are such that the time required for moving the disk 5 through an angular distance of l is about I to 2 hours. Consequently the time required for moving'the date number ring 1' through an angular distance of 360l3l, i.e., the time required for replacing the date number appearing in the inspection window G by the following date number, is likewise about 1 to 2 hours.

It should be noted that with the described date indicating mechanism the date number ring 1 will remain locked not only when it is kept in its rest position by the pair of pins 8A and 8B engaging in two adjacent slits 4 and by the pair of pins 8A and 7Aengaged by thecircular peripheral portion of the cam 11, but also during the angular movement of the date number ring 1 imparted thereto by the pin 8A or 88 on the disk 5, the projection l8 on the'circular cam 11 or the recess 16 or 17 in which engage the pins of the disk 5, the angular position of the circular cam l 1 being controlled by the gear train of the watch. I

The previously mentioned reciprocal magnetic attraction between the pins 8A and 88, on the one hand, and the date number ring 1, on the other, occurs irrespective of the angular position of the disk 5, i.e., irrespective of the degree of penetration of the pin 8A or 88 into one of the slits 4 in the date number ring 1. Therefore, this pin will always be in material engagement with a portion of one edge of the slit so as to eliminate the influence of the play which may exist between the pins'and the teeth of the date number ring 1.

It should further be noted that all members of the described drive mechanism have a symmetrical configuration so that this drive mechanism can be used both for moving the date number ring 1 in a clockwise 8B and the teeth 1C direction, as described above, and for moving the date number ring in an anticlockwise direction, particularly when it is desired to change the date appearing in the inspection window G by actuation from the outside of the watch, for example, by means of the time adjusting device of the watch.

All elements of the described mechanism have a particularly simple structure so that they can be easily and inexpensively produced and mounted. Further the operation of this mechanism is of great simplicity and this guarantees good working and small wear of the mechanism over a long period of time.

Finally, as the date number ring 1 has a very simple geometric serrated configuration formed by the series of teeth 1C defined by the'slits 4 with their open ends on the inner edge of the date number ring, and as the drive pins 7A, 7B,.8A, and 88 on the disk 5 have a shape which can be easily produCCd, the play in the angular displacement of the circular cam 11 may be very small. Further, due to the disposition of the disk 5 carrying the pins 7A, 78, 8A and 88, a radial play which may exist in the positioning of the date number ring 1 will produce only a very small angular play of the date number ring. a

lt is to be understood that the invention is not limited to the described and illustrated embodiment and that numerous changes and modifications may be made therein without departing from the scope of the invention. In particular, the described date indicating mechanism could very well be produced without a permanent magnet 9, but in such a mechanism evidently the play which may exist between the pins 7A, 7B, 8A,

and the date number ring 1 cannot be taken up. r

Further, it'would also be possibleto provide a date indicating mechanism in which the date number ring. 1 has slits 4 located with their open ends on the outer edge of the date number ring 1, as shown in FIG. 9. in this case the disk 5 and the rotatable circular cam 11 are mounted on shafts extending with their axes at right angles to the outside edge of the date number ring 1 in a plane-forming a dihedralangle of 45 with the plane passing through the axis of rotation of the disk. 5 and the axisof symmetry of the date number ring. 1.

The date indicating mechanism of the present invention can be used for mechanically operated watches as well as electromechanically or electronically operated watches.

- lclaim:

1. In a date indicating mechanism for watches, of the type havinga rotatable date number ring carrying on one side n datenumbers equidistantly spaced over the entire circumference of the ring and means for periodically driving the ring through an angular distance corresponding to 360/n past an inspection window permitting the date numbers on the ring to be individually and successively observed, the improvement of said drive means comprising a series of n slits equidistantly spaced around the circumference of the rotatable date number ring, said slits being open at one edge of the date number ring and having parallel longitudinal edges, a longitudinal axis oriented toward the center of the date number ring, and a radial length substantially corresponding to half the distance between the two points of intersection between the two opposedlongitudinal edges of two adjacent ones of said slits and the edge of the date number ring containing the open ends of said slits;

a disk located in a plane extending parallel to the plane of the date number ring and rotatably mounted on a shaft centered substantially at right angles to the edge of the date number ring containing the open ends of said slits; said disk carrying four equidistantly angularly spaced pins each spaced from the axis of said shaft of said disk by a distance substantially corresponding to half the distance between the two points of intersection of the two adjacent longitudinal edges of two neighboring ones of said slits in the date number ring with the edge of the latter containing the open ends of said slits, the width of said pins being substantially equal to that of said slits; said pins, located in diametrically opposed positions on said disk with respect to the axis of rotation thereof, having a projecting portion of a length at least greater than the distance between the adjacent surfaces of said date number ring and said disk, the other two of said pins having a projecting portion of a length smaller than said distance;

a rotatable substantially circular cam located in a plane extending parallel to the plane of said date number ring and having an operative profile composed of a first and a second portion, said first portion extending in a circular'direction around the axis of rotation of said rotatable cam and being designed for locking said date number ring in one of its n angular positions, the axis of rotation of said rotatable cam being positioned so that said first portion of the rotatable cam will engage two neighboring ones of said pins on said disk;

said second portion of said rotatable cam being designed for moving said date number ring from a given angular position to the next one and including a radial projection having a width corresponding at most to the distance between two neighboring ones of said pins, and two recesses arranged one on each side of the radial projection and having a width at least corresponding to that of said pins, and

a kinematic chain for moving said rotatable cam by one revolution each 24 hours from the gear train of the watch.

2. A date indicating mechanism as claimed in claim 1, wherein said disk and the two shorter pins mounted thereon are made of non-magnetic material whereas the two longer pins are made of magnetizable material and are secured with one of their ends in holes extending through the thickness of said disk so as to terminate with said ends flush with the surface of said disk opposed to the surface of said disk carrying said projecting portions of said pins, a magnetizable armature is located in front of said surface of said disk opposed to number ring near the region thereof where said magnetizable pins engage said slits in said date number ring, so that at least one of said magnetizable pins is permanently maintained in engagement with said date 3,704,583 9 10 number ring due to the magnetic attration exerted therebetween, irrespective of the angular position occupied by said pin carrying disk.

.-..- mmno 7 mm 

1. In a date indicating mechanism for waTches, of the type having a rotatable date number ring carrying on one side n date numbers equidistantly spaced over the entire circumference of the ring and means for periodically driving the ring through an angular distance corresponding to 360*/n past an inspection window permitting the date numbers on the ring to be individually and successively observed, the improvement of said drive means comprising a series of n slits equidistantly spaced around the circumference of the rotatable date number ring, said slits being open at one edge of the date number ring and having parallel longitudinal edges, a longitudinal axis oriented toward the center of the date number ring, and a radial length substantially corresponding to half the distance between the two points of intersection between the two opposed longitudinal edges of two adjacent ones of said slits and the edge of the date number ring containing the open ends of said slits; a disk located in a plane extending parallel to the plane of the date number ring and rotatably mounted on a shaft centered substantially at right angles to the edge of the date number ring containing the open ends of said slits; said disk carrying four equidistantly angularly spaced pins each spaced from the axis of said shaft of said disk by a distance substantially corresponding to half the distance between the two points of intersection of the two adjacent longitudinal edges of two neighboring ones of said slits in the date number ring with the edge of the latter containing the open ends of said slits, the width of said pins being substantially equal to that of said slits; said pins, located in diametrically opposed positions on said disk with respect to the axis of rotation thereof, having a projecting portion of a length at least greater than the distance between the adjacent surfaces of said date number ring and said disk, the other two of said pins having a projecting portion of a length smaller than said distance; a rotatable substantially circular cam located in a plane extending parallel to the plane of said date number ring and having an operative profile composed of a first and a second portion, said first portion extending in a circular direction around the axis of rotation of said rotatable cam and being designed for locking said date number ring in one of its n angular positions, the axis of rotation of said rotatable cam being positioned so that said first portion of the rotatable cam will engage two neighboring ones of said pins on said disk; said second portion of said rotatable cam being designed for moving said date number ring from a given angular position to the next one and including a radial projection having a width corresponding at most to the distance between two neighboring ones of said pins, and two recesses arranged one on each side of the radial projection and having a width at least corresponding to that of said pins, and a kinematic chain for moving said rotatable cam by one revolution each 24 hours from the gear train of the watch.
 2. A date indicating mechanism as claimed in claim 1, wherein said disk and the two shorter pins mounted thereon are made of non-magnetic material whereas the two longer pins are made of magnetizable material and are secured with one of their ends in holes extending through the thickness of said disk so as to terminate with said ends flush with the surface of said disk opposed to the surface of said disk carrying said projecting portions of said pins, a magnetizable armature is located in front of said surface of said disk opposed to the surface of said disk carrying said projecting portions of said pins, said date number ring is made of magnetizable material, and a permanent magnet is arranged between said armature and a region of said date number ring near the region thereof where said magnetizable pins engage said slits in said date number ring, so that at least one of said magnetizable pins is permanently maintained in engagement witH said date number ring due to the magnetic attraction exerted therebetween, irrespective of the angular position occupied by said pin carrying disk. 